Die casting apparatus



Dec. 5, 1967 w. SMITH DIE CASTING APPARATUS Filed May 2, 1966 Ill Inventor: Loren W. Smith mmm/mm;

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his Aitorney -the molds themselves be nited Sttes 3,35,l3l Patented Dec. 5, 1967 3,356,131 DIE CASTING APPARATUS Loren W. Smith, Eggertsville, NSY., assigner to Symington Wayne Corporation, Salisbury, Md., a corporation ot' Maryland Filed May 2, 1966, Ser. No. 546,993 11 Claims. (Cl. 164-314) i ABSCT F THE DISCLSURE This invention relates to die casting apparatus and this application is a continuation-impart of my copending application Ser. No. 444,459, tiled Mar. 31, 1965.

The above copending application discloses a method `of casting a run of metal castings in metal molds in a plurality of casting operations of usually identical molds is used and expended in each operation. While applicable generally to the casting of metals in metal molds, the method is particularly adapted for casting high melting metals, such as the ferrous metals, brass and bronze, in molds made of relatively low melting metals, such as aluminum and its alloys, and has the salutary effect of freeing the run of castings from dependency for preciseness on the life of a single mold. To be usable in the method, the metal mold must be of such thermal diffusivity and mass as to maintain its inin which one of a plurality ytegrity to the point of freezing to shape of the metal cast therein.

The method especially lends itself to die casting in which the metal being cast is injected under pressure into the metal mold and in such use it is desirable that die castable, so that they can be supplied at the rate at which the f are expended and thus make it unnecessary to start the run with a large stock of molds on hand. Aluminum and its alloys, termed generally aluminum, are mentioned in the cepending application as particularly suited for use as the mold metal in die casting metals according to the method, in combining high thermal diffusivity and ready die castability in permanent metal molds with inertness to ferrous and other high melting metals.

As explained in the above application, the expendable metal mold, to maintain its integrity to the point of freezing to shape of the cast metal, must have suicient mass to absorb the heat of the cast metal unless provision is made for rapid dissipation of heat during the casting operation. Dependence solely upon the mass of the expendable metal mold to dissipate the heat of the cast metal, while effective, can prove uneconomical for casting large or complex-shaped castings in correspondingly complicating both the casting of the expendable molds and the preferred reuse of the mold metal.l

Although in die casting the low melting metals in permanent molds, aluminumv is. sometimes the mold metal,

the general practice is to make the permanent molds of steel because of the longer mold life usually derived from that metals greater wear-resistance and much higher melting point. As a mold faced or lined with steel will have substantially the same permanence as an all steel mold, a permanent mold for die casting low melting metals on occasion may have a steel facing and a backing of some lower melting metal of suitable thermal con ductivity, with the bulk of the backing such that it can act as a heat sink and absorb the heat of the cast metal transmitted to it through the facing.

It is recognized that when two metal layers simply abut against each other there will be a sharp drop in the overall heat conductivity, presumably due to the presence of a thin film or pockets of air at the interface between the layers. For permanent composite molds this problem is readily solved by bonding the layers over the entire interface by solder or a like bond, which, by fill-ing all voids, effectively eliminates any otherwise interposed air. However, where, as in the method of my copending application, a mold is expended in each casting operation, it is not feasible to bond the expendable mold to a backing and the presence of the inevitable air at the interface would appear to bar a reduction in the mass 0f the expendable mold by backing it by a permanent heat sink.

It is quite customary to reduce the mass of the mold metal in a permanent die casting mold by the forced circulation of water or other fluid under pressure either through or around the mold both during and betwee casting operations. The diiculty in the case ofthe method of my copending application is that each expendable mold must be removed and replaced at the end of each casting operation and this is not practical if the mold is exposed to circulating fluid during a casting operation.

The primary object of the present invention is to provide apparatus for casting metals in expendable metal molds whereby the mass of the expendable molds is able to be reduced by backing them by a permanent heat sink and bonding of each mold to the heat sink is not required to avoid a drop in thermal conductivity of the usual order across the interface.

Another object of the invention is to provide apparatus for casting metals in expendable metal molds whereby tbe expendable molds are backed by a permanent heat sink and, instead of bonding each mold to the heat sink, any air in the interface therebetween is replaced by liquid of relatively high heat conductivity inert to the molds and heat sink, thereby not only correspondingly increasing the heat conductivity across the interface but preventing any reduction in that conductivity by oxidation of the presented surfaces of the mold and heat sink.

A further object of the invention is to provide apparatus for casting metals in expendable molds wherein a permanent heat sink backing each mold has its mold-receiving seat lined with a heat conductive liner of such construction as to permit a heat conductive liquid to flow under pressure between a mold and the heat sink during a casting operation and yet prevent leakage of the liquid on subsequent removal of the mold.

A further object of the invention is to provide apparatus for casting metals in expendable metal molds wherein the expendable molds are backed by but not bonded to a permanent heat sink and the heat conductivity across the interface is improved and heat from the heat sink is absorbed by the forced circulation of fluid which is automatically circulated only during a casting operation, thereby permitting reduction of the masses of both the molds and the heat sink.

Other objects and advantages of the invention will appear hereinafter in the detailed description, be particularly pointed out in the appended claims and be illustrated in the accompanying drawings, in which:

FIGURE 1 is a central vertical sectional view, in part diagrammatic, of a preferred embodiment of the casting apparatus of the present invention;

FIGURE 2 is a fragmentary vertical sectional View on a larger scale taken along lines 2-2 of FIGURE l; and

FIGURE 3 is a fragmentary perspective view on the section -of FIGURE l and scale of FGURE 2, showing a corner portion of the inner chamber about the mold.

Referring now in detail to the drawings in which like reference characters designate like parts, the improved apparatus of the present invention for die casting metals in expendable metal molds in accordance with the method of my copending application Serial No. 444,459, is comprised of a permanent heat sink 1 and a plurality of expendable molds 2 interchangeably seatable in the mold holder and each expended in a single casting operation. Made of copper or other metal of suitable heat conductivity and resistance to distortion by the heat to which it will be `subjected in a casting operation, the heat sink 1 is split or separable for separation vertically or more preferably horizontally into a plurality of holder members or parts. The heat sink 1 preferably is a combined mold holder and heat sink and will usually have two parts. While the parts are relatively reciprocable and both may be movable, the illustrated heat sink and holder has one part 3 stationary and the other part 4 movable.

To facilitate its separation, the illustrated split heat sink and holder 1 is mounted on a suitable stand or support 5 having a base 6 supporting bot-h parts 3 and 4 and an upright 7 backing and having fixed or secured to it the movable part 4. Slidable or reciprocable horizontally along the base 6, the movable part 4 may be guided in its movements, to ensure its alignment with the stationary part 3, by slidably mounting it on guide rods 8 fixed at one end to the upright 7 and extending horizontally through both holder parts adjacent their corners. Conveniently, the movable part 4 is moved or powered by a fluid-actuated piston 9.

Made of aluminum or its alloys, herein generally termed aluminumj or other suitable, high heat conductivity metal, each expendable mold 2 also is split or separable, preferably into two parts 10, each of which is removably seatable or receivable in a socket, cavity or seat 11 of corresponding, desirably non-round configuration in and preferably centered laterally on the confronting or inner faces, surfaces or ends 12 of the holder parts 3 and 4. In turn, the mold parts together bound a mold cavity 13, which, depending on the castings being die cast in a particular run, may be a single cavity or a plurality of gate-connected cavities, and that cavity or cavities usually will be formed in part in the confronting or inner face 14 of each mold part.

In the illustrated apparatus, both the heat sink and mold holder 1 and each expendable mold 2 are each split along a parting line indicated at 1S and adapted to have the inner faces 12 and 14 of its parts 3 and 4 and 10, respectively, close or contact along that line on closing of the mold and clamping of its parts together for a casting operation under the closing or clamping pressure applied by the fluid-actuated piston 9. When a mold 2 is closed, it thus is completely enclosed by the mold holder 1. When seated in the mold holder, each expendable mold is spaced inwardly therefrom, as by spacers 16, to provide therebetween a thin chamber, space or pocket 17 substantially completely surrounding the mold. The preferred mold holder 1 is fluid-cooled and for this purpose has suitably jacketed or enclosed chambers or tanks 18 covering at least the outer ends or surfaces 19 of its parts 3 and 4.

The end chambers 18, of course, enable the mold holder 1, while acting as a heat sink for each expendable mold 2, itself to be cooled by so-called sweat cooling and thus be of less mass than if it were exposed only to still ambient air. However, the purpose of t-he inner space or chamber 17 about the expendable mold 2, is quite different. With the need to insert a new mold in the mold holder at the beginning of each casting operation in carrying out the method of my copending application, it is not feasible either to solder or otherwise bond each mold to the holder or rely on preciseness of fit to eliminate air in the interface therebetween. But if, as in the apparatus of this invention, the mold is surrounded or spaced from the holder by a thin chamber and water or other liquid of high heat conductivity relative to air fills any voids in and is circulated through that chamber at a rate at which it will not vaporize under the heat received by it from the mold during a casting Operation, the usual drop in heat conductivity across an interface or joint between unbounded metal surfaces is drastically reduced. The preferred liquid is a non-oxidizing or inert liquid, again such as water, which, by continuously washing the presented or confronting surfaces of the mold and holder bounding the chamber 17 during a casting operation, will effectively prevent the building up of a low conductivity oxide layer on t-hose surfaces while they are heated by the cast metal, the effect being particularly beneficial in the case of the permanent holder because it, unlike the onetime expendable mold, must be so heated many times.

For circulating fluids therethrough, the end and inner chambers 18 and 17 are suitably fitted for feeding and draining and preferably fed from the bottom and drained from the top. To accommodate the volume of the liquid required to prevent vaporization despite the thinness of the stream flowing around the mold 2, the inner chamber 17 preferably has at least two or a pair of inlet pipes or passages 20 and the corresponding number of outlet pipes or passages 21, one of each in and extending from bottom or top through each of the stationary and movable holder parts 3 and 4. To accommodate the transition from the usual circular cross-section to the thin chamber without reducing its free cross-sectional area, each of the pipes 20 and 21 preferably has a flared or fan-shaped mouth 22 opening inwardly onto that chamber.

Since separate, the end chambers 18 should have separate inlet and outlet pipes or passages 23 and 24, respectively, one of each, connected or opening onto its lower or upper end, as appropriate, ordinarily suflicing for each chamber. If, as in the disclosed embodiment, t-he inlet pipes 20 and 23 for the inner and end chambers 17 and 18 lead upwardly thereto through the base 6, those leading to or through the stationary holder part 3 may be continuous or uninterrupted but those leading to or through the movable holder part 4 should be interruptable at the joint between the base 6 and the movable part to allow for or accommodate movement of the latter between open and closed positions. With a sliding fit between the movable holder part 4 and the base 6, the interruption or joint between the outer or base and inner or holder sections of each of the inlet pipes 20 and 23 related to the movable part may be a sliding joint, with an O-ring or like gasket 26 in the base or movable part about its section at the joint for sealing between the sections on alignment thereof in the closed position of the holder part.

The piping for the apparatus is simplified, when, as illustrated, the same fluid medium, either water or other suitable fluid, is used as the cooling medium for the end chambers 18 and the heat transfer medium for the inner chamber 17. In such case, the inlet pipes 20 and 23 Iand outlet pipes 21 and 24 may have or be connected, respectively, to a common inlet line 27 and a common outlet line 28. With this arrangement, a flexible link 29 in the outlet line 28 between the stationary and movable outlet pipes 21 and 24 will accommodate the movements of the movable holder part 4, whi-le Ia valve 30 in the outlet line 27 between the inlet pipes 20 and 23 and a source (not shown) enables the ow of fluid to the inlet pipes to be cut on and olf as desired.

Cutting olf of the valve 30 will stop the circulation of uid through the inner and end chambers 17 and 18 but, while reducing the pressure thereupon, it will not eliminate the fluid in the chambers. Consequently, if, as might have been implied from the previous description, the inner chamber 17 is open except for spacers 16, since it is Ibounded inwardly by the mold 2, the fluid in the space will gush or at least leak out as the mold is being removed. This very undesirable result is eifectively eliminated by employing as the spacers 16, liners or jackets which ll the chamber or space 17 about the mold 2 and are of such porosity as to pass iluid only when it is under a pressure above -a predetermined minimum, which in the usual case may be somewhere around 90 lbs. p.s.i. Permanent and lining the sockets 11 in the holder pa-rts 3 and 4 and soldered or otherwise bonded, secured or attached thereto, so as to remain in place when the mold parts are removed, the porous liners 16 preferably are made of pressed powdered metal in which high conductivity is readily combined with controlled porosity for producing a valving action.

For charging the mold cavity 13 with liquid metal during a casting operation, the apparatus includes a charging unit 31. The cavity 13 preferably is chargeable from either the side or the bottom and in the usual m-anner the mold 2 will have in it suitable vent holes (not shown) for venting the air displaced from the cavity by the injected metal. The illustrated charging unit 31 is adapted to charge the mold cavity 13 from the side and conveniently is mounted on the stand 5 beyond the upright 7. A charging cylinder 32 in the unit 31 of =a volume to hold a metered charge of liquid metal suicient to ll the cavity 13 is connected to the cavity through a tubular nozzle or feed tube 33 on the unit which leads through the upright 7 and stationary holder part 3 to the mold part 10 seated therein. The unit 31 preferably is heat insulated from the mold 2 by a ceramic collar 34 fitting in the stationary mold part and on the end of the nozzle 33 and here containing the gate 35 to the mold cavity.

A reciprocable plunger 36 projecting into the charging cylinder 32, is 'actuatable by a fluid, usually air, for driving or injecting the liquid metal from the cylinder into the mold cavity 13. introduction of the actuating air through an air inlet line 37 is controlled by a suitable valve 38. Since the liquid metal otherwise could iiow from the charging cylinder 32 through the nozzle 33 into the mold cavity 13 before the plunger 36 was actuated, it usually will be desirable to block such premature ow by a suitable means, such as the illustrated controlled burst diaphragm 39, which here conveniently is seated in the collar 34 at the end of the nozzle. To act as intended, the preferred diaphragm 39 is a thin disc of a metal that will not be melted by the heat of the molten metal and -at the same time will give or rupture under the pressure applied by the plunger 36 in injecting the molten metal into the mold cavity 13.

In the operation of the apparatus, an expendable mold 2 will have its parts 10 seated in the sockets 11 in the holder parts 3 and 4 at the start of a casting operation and the piston 9 will then be actuated to yclose the mold. At this juncture, the plunger 36 is actuated to inject the liquid metal from the charging cylinder 32 into the mold cavity 13 and concurrently water or other uid is circulated under pressure through the inner chamber 17 and end chambers 18. The concurrence in the inception of the injection of the liquid metal and circulation of the uid through the chambers 17 and 18 should also apply to their duration, so that the metal in the mold cavity 13 will be under pressure and the liuid continue to circulate at least until the cast metal has cooled to the point of freezing to shape. This is here accomplished by making the valves 30 and 38 solenoid-actuated valves connecter in series and controlled in opening and closing by a com mon switch 40. After the cast metal has frozen to shape the switch 40 is opened to relieve the pressure on the plunger 36 land the circulating fluid, whereupon the holder parts 3 and 4 are separated by actuation of the piston 9. Removal of the mold 2 and casting completes the operation, except for the preferred reuse of the meld metal to make new molds and any finishing required on the casting.

From the above detailed description it 'will be apparent that there has been provided an improved apparatus for casting metals in expendable metal molds, which, by effectively absorbing the heat of the cast metal to the point of freezing, to shape at least in part by a heat sink, enables the mass of the mold to be minimized, with consequent versatility in the size and shape of the castings that can be produced. It should be understood that the described and disclosed embodiment is merely exemplary of the invention and that all modifications are intended to be included that do not depart from the spirit of the invention and the scope of the appended claims.

Having described my invention, I claim:

1. Apparatus for die casting metals in expendable metal molds comprising a separable metal heat sink, an expendable metal mold removably mounted in said heat sink in spaced relation thereto, a liquid heat transfer medium having a higher heat conductivity than air lling all voids in the space between said heat sink and mold during a casting operation, means for circulating said liquid medium under pressure through said space during said operation at a rate to prevent vaporizing of said medium and means for preventing said medium from circulating through said space except when the pressure thereon is above a predetermined level.

2. Apparatus according to claim 1 wherein the preventing means is a heat conductive porous liner in the space between the mold and the heat sink.

3. Apparatus according to claim 2 wherein the circu- 'lating means is operative only during a casting operation, the heat sink has a seat thereon outwardly bounding the space therebetween and the mold, the liquid medium is injected into the space through said seat, and the liner permanently lines said seat and is of a porosity to prevent leakage of said liquid medium therethrough on removal of the mold at the completion of the casting operation.

4. Apparatus according to claim 3 including liuidactuated means for injecting liquid metal under pressure into a mold cavity in the mold, and means operatively connecting the circulating and said injecting means for preventing operation of said circulating means except when actuating iluid is applied to said injecting means.

5. Apparatus according to claim 3 wherein the liner space-s the mold from the heat sink.

6. Apparatus according to claim 5 wherein the liner is a powdered metal liner.

7. Apparatus according to claim 5 wherein .the separable heat sink is a combined heat sink and mold holder of which parts are separable for insertion and removal of the mold respectively Vat the start and finish of the casting operation in which the mold is expended, the expendable mold is one of a plurality of expendable molds interchangeably seated in the heat sink and each seated therein during only a single casting operation, each mold is made of a plurality of parts each seatable in a part of the heat sink, and clamping pressure for clamping said parts of each mold together during a casting operation is applied thereto through the heat sink.

A8. Apparatus according to claim 2 including chamber means on said heat sink, and means for circulating a uid coolant under pressure through said chamber means for cooling said heat sink during a casting operation.

9. Apparatus according to claim 8 wherein the liquid medium `and fluid coolant circulated respectively through the space between the mold and the heat sink `and through the chamber means of the heat sink are both water` 10. Apparatus according to claim 9 wherein the eX- pendable mold is aluminum `and lthe heat sink is copper.

11. Apparatus raccording to claim 8 wherein the heat sink has its vparts mounted on a base one part stationarily and another part for reciprocable movement relative to the one part, and the means for circulating the liquid medium through the space between the mold :and the heat sink and the fluid coolant through the chamber means are operatively connected to fluid-actuated means for in- UNITED STATES PATENTS 8/1928 Wood 249-135 6/1950 Renaud 249-79 I. SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Assistant Examiner. 

1. APPARATUS FOR DIE CASTING METALS IN EXPANDABLE METAL MOLDS COMPRISING A SEPARABLE METAL HEAT SINK, AN EXPENDABLE METAL MOLD REMOVABLY MOUNTED IN SAID HEAT SINK IN SPACED RELATION THERETO, A LIQUID HEAT TRANSFER MEDIUM HAVING A HIGHER HEAT CONDUCTIVITY THAN AIR FILLING ALL VOIDS IN THE SPACE BETWEEN SAID HEAT SINK AND MOLD DURING A CASING OPERATION, MEANS FOR CIRCULATING SAID LIQUID MEDIUM UNDER PRESSURE THROUGH SAID SPACE DURING SAID OPERATION AT A RATE TO PREVENT VAPORIZING OF SAID MEDIUM AND MEANS FOR PREVENTING SAID MEDIUM FROM CIRCULATING THROUGH SAID SPACE EXCEPT WHEN THE PRESSURE THEREON IS ABOVE A PREDETERMINED LEVEL. 